1. Field of the Invention
This invention relates to the display of counted totals to be monitored at a remote location with the information to be transferred by radio telemetry to a display station.
2. Discussion of Related Art
It is often desirable to monitor an event at one location, transmit the monitored information to a second location without the use of wires or mechanical connections and display the transmitted information. One application of such a system can readily be understood with respect to self-service filling stations wherein a single attendant must keep track of amount of fuel being pumped by each customer. Since the attendant is unable to see the individual pump registers, it is necessary to transmit the information from each customer-operated pump to a central control and display panel. Obviously, this information must be transmitted accurately and a continuous update of the counted total of fuel pumped is necessary to insure that the final charge to the customer is accurate.
Other examples wherein monitoring and remote display of a counted total is desirable include counting the number of products moving down an assembly line and monitoring outputs of hospital equipment. In this latter example, it would be desirable to allow a portable display to be carried by, for instance, hospital personnel who are required to monitor the hospital equipment but are not fixed at a given permanent location.
Certain remote monitoring systems have been suggested. For instance, U.S. Pat. No. 3,609,729, issued Sept. 28, 1971 to Anderson, shows a telemetry system wherein a numerical count proportional to a parameter is momentarily stored in a series arrangement of multi-stage counters. The information in the counters is transmitted using pulse position modulation, a receiver decodes the information and records it on a strip chart recorder. U.S. Pat. No. 3,659,277, issued Apr. 25, 1972 to Brown, shows a receiver transmitter apparatus including a hard wired connection between the receiver and transmitter. The transmitter provides an output pulse train, the repetition rate of which is proportional to the amplitude of the signal of the transmitter input. Also, power for the transmitter is derived from the receiver through the hard wired connection. U.S. Pat. No. 3,786,423, issued Jan. 15, 1974 to Martell, discloses a method and apparatus for remotely reading one or more meters from a central location. The meter information is supplied to an accumulator, the information from which is placed into a shift register and sequentially shifted out into a frequency shift keying oscillator where frequency is encoded and transmitted via telephone lines to a central station. U.S. Pat. No. 4,119,948, issued Oct. 10, 1978 to Ward et al, shows a remote meter reading system which includes an electro-optical transponder effective to receive and transfer data from a monitor unit and to convert the data into a train of laser radiation pulses which are emitted in response to interrogation by a laser radiation pulse from a remote mobile interrogator unit. U.S. Pat. No. 4,194,177, issued Mar. 18, 1980 to Adamson, shows a system for continuous monitoring of liquid levels in storage tanks. The system includes a differential pressure cell in circuit with a digital volt meter which in turn is connected to a series of look-up, read only memories (ROM). The digital volt meter continuously applies BCD signals to the ROMs. The ROMs retain in memory the gray code translation of the BCD input and are periodically accessed via an analog multiplexer.